The last time we heard from country star Dierks Bentley, everything was hunky-dorky.

It was the summer of 2009 and the Arizona pretty boy was preening on the top of the charts with "Sideways," a doofy party anthem where the singer's notion of fun felt too good, too clean. It had all the charm of celery.

And that's why Bentley's new album, "Up on the Ridge," qualifies as a both major transformation and minor miracle. The 34-year-old singer has always had a fine ear for hooks, but this time out, he's swaddled them in traditional, bluegrass-inspired arrangements. The results are dazzling -- and for a chart-topping cutie-pie, it's a supremely gutsy move. To prove he means it, he's allowed his neatly trimmed stubble to sprout into a mangy scruff.

But facial hair does not a great album make -- so Bentley mustered a gang of esteemed collaborators for what might be the best country recording we'll hear in 2010. He harmonizes with Vince Gill and Alison Krauss. He duets with Kris Kristofferson and Del McCoury. He covers Bob Dylan and U2. All without flinching.

The singer's poise is particularly impressive with "Bad Angel," a swaggering, roadhouse-ready tune about facing down addiction. Flanked by Miranda Lambert and Jamey Johnson -- two of Nashville's heirs to the outlaw country mantle -- Bentley holds his own. "I'm standing at the crossroads of temptation and Salvation Street," he sings, his voice packing enough bravura, you actually believe that he's not only been to the bottom -- he's going to pull through, too.

Could this really be the same guy who spent the past decade spritzing the airwaves with cuddly pop-country? To be fair, Bentley has always had a penchant for bluegrass, but his albums have only explored the genre one or two tracks at a time. Surrounded by lukewarm love songs (2005's "Come a Little Closer," 2008's "Feel That Fire") and middling travel tunes (2006's "Every Mile a Memory" and "Long Trip Alone"), his more bluegrassy fare often felt obligatory -- or even worse, like a halfhearted grab for credibility.

After this album, cred should never be a problem for Bentley. Even more exciting than the singers he snagged for this recording are the tunes he chose to croon with them. He teams up with Chris Thile -- formerly of newgrass heroes Nickel Creek and currently of the Punch Brothers -- for Dylan's "Señor (Tales of Yankee Power)." Together, they speed up the search for "where she's hiding," but still arrive, sunburned and delirious, at Dylan's lyrical dead end. "This place don't make sense to me no more," Bentley sings.

Rarely is covering U2 riskier business than tinkering with Dylan, but Bentley's bluegrass version of "Pride (In the Name of Love)" feels brave and surprising. McCoury picks away throughout, transposing the Edge's chiming guitar riffs into something simpler, without sacrificing elegance. Squint your ears and you might even hear the ties that connect a Dublin-born rock troupe to an Irish diaspora that once germinated bluegrass across Appalachia.

And there's more: Tragic work songs and pleading love songs. "Down in the Mine" feels particularly harrowing in light of the mining catastrophe that took the lives of 29 men in West Virginia in April, while "Draw Me a Map" finds Bentley softly pining for a route back to his lost lover's doorstep, those clarion pipes sounding more genuine than ever.